1. Field of the Invention
In general, the present invention relates to a device, system and method of casing while drilling for oil and gas utilizing a measurement while drilling tool. More particularly, the present invention provides a system to position a measurement while drilling tool in the casing while drilling with the casing and retrieve the same without bringing up the casing to the surface.
2. Description of the Prior Art
Most oil and gas wells are typically drilled with drill pipe and then later cased in with a type of pipe referred to as casing. It is also known to not use drill pipe, but to actually drill with casing, which is sometimes referred to as casing drilling or casing while drilling (CWD). The main purpose of casing drilling is to eliminate classic casing runs and isolate formations while drilling. By using standard casing string instead of conventional drill string, the drilling and casing are executed simultaneously, section by section. Casing while drilling is also a hazard mitigation solution, having applicability in drilling soft shallow sections with high bore hole instability and known losses.
Casing while drilling is more efficient because it is essentially two operations in one with each meter drilled and cased at the same time. Further, it reduces time for tripping in and out as well as the risk involved with such. Still further, it reduces drilling time, cementing time, and overall non-productive time.
Casing while drilling does present other challenges over standard drilling operations. Whereas a drill string in conventional operations is pulled up out of the well at some point, the casing while drilling pipe is never pulled up meaning that the drill bit is permanently left in the hole. Furthermore, all drilling operations require some type of downhole tool for determining where the drilling is and going. MWD stands for “measurement while drilling” in the oil and gas industry. The trajectory of the drilling obviously needs to be determined as well as specific information such as direction, angle, and downhole conditions and MWD tools are utilized to provide this information.
In the prior art utilizing drill pipe, MWD tools are installed as part of the bottom hole assembly (BHA) near the drill bit. The tools are either contained inside a thick walled, drill collar or they are built directly into the collars at a factory prior to arriving on the drilling location. Most MWD tools have a diameter of about the same size of a drill string, which may be around 3½ inches although other sizes are known. After the drilling is complete, the drill pipe is removed from well along with the MWD tool before the casing and well production starts. It is not desirable to leave the tool permanently at the bottom of the well.
Casing are of a larger diameter than the drill string by logical definition. It is not uncommon for casing near the bottom of the well to be at least 5½ inches and more typically 6½ inches.
Thus, there is a need for a system that allows a standard MWD tool to be placed in a casing while drilling operation and allows the MWD tool to be removed from the bottom of the well without pulling the casing from the well. The above discussed limitations in the prior art is not exhaustive. The current invention provides an inexpensive, time saving, more reliable apparatus and method of utilizing a MWD tool in a casing while drilling operation where the prior art fails.